10 



wood worthless for finishing, staves, and woodenware, but apparently is 

 not seriously detrimental to timber for other purposes. 



(2) The black check is caused in nearly every case by an injury to 

 the cambium (growing layer) of the trunk by the hemlock bark maggot, 

 Oheilosia alaskensis Hunter. Somewhat similar defects may be caused 

 by barkbeetles, bark-bqrers, sapsuckers, or anything that makes a 

 wound in the cambium, which afterwards heals. 



(3) The maggot enters the bark through an abandoned food burrow 

 made by the hemlock barkbeetle {Hylesinus n. sp.). It gradually 

 enlarges the burrow into a small wound, in which it lives for several 

 years, feeding on the sap and cambium. In the spring, when full 

 grown, it pupates in the resin mass which has formed on the outer bark 

 around the entrance to the wound. The puparium soon changes to the 

 adult, which emerges in April or May. The egg is probably laid on the 

 resin exuding from the abandoned gallery of the barkbeetle. 



(4) A near relative (Oheilosia hoodianus Bigot) of the hemlock 

 bark maggot causes, in a similar manner, a black check in the timber 

 of lowland, grand, or white fir (AMes grandis). It enters the bark 

 through the abandoned food burrows of several species of barkbeetles. 



(5) The alpine fir (Abies lasiocarpa), the Sitka spruce (Picea sitch- 

 ensis), and probably many other trees are injured more or less by bark 

 maggots that enter wounds and enlarge them or keep them open until 

 the conditions are such that checks form in the timber. 



(6) For preventing losses in timber cut for purposes requiring clear 

 stuff, select trees growing at altitudes above 1,800 feet and those at 

 lower elevations which are free from the black indicating spots (old 

 resin masses) on the bark. 



Approved : 



James Wilson, 



Secretary of Agriculture. 



Washington, D. C, May 24, 1905. 



O 



